In a typical communications network, also referred to as a wireless communications system, wireless communications network, a cellular network, a communications network or a communications system, a device, communicates via a Radio Access Network (RAN) to one or more Core Networks (CNs).
The device may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operators radio access network and core network provide access, e.g. access to the Internet. The device may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The device may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another device or a server.
Devices are enabled to communicate wirelessly with the communications network. The communication may be performed e.g. between two devices, between a devices and a regular telephone and/or between the devices and a server via the radio access network and possibly one or more core networks and possibly the Internet.
The communications network covers a geographical area which may be divided into cell areas, and therefore also called a cellular network. Each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. evolved Node B (eNB), eNodeB, NodeB, B node, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base station communicates with the device within range of the base station.
The device may be in different modes: idle mode or connected mode. A mode may also be referred to as a state. In idle mode, the device is e.g. not in a call, i.e. the device is not “doing anything” and does not have any context activated. When the device is in connected mode, it is in e.g. a call, i.e. the device is “doing something”. Data is transmitted between the device and the network only when the device is in connected mode.
In addition to the device, the communications network comprises a plurality of nodes in the access network and the core network. Such nodes may be for example a GGSN, SGSN, MME, PGW or SGW. GGSN is an abbreviation of Gateway GPRS Support Node and SGSN is an abbreviation of Serving GPRS Support Node, where GPRS is an abbreviation for General packet radio service. MME is an abbreviation of Mobility Management Entity. PGW is an abbreviation of PDN Gateway, where PDN is an abbreviation of Packet Data Network. SGW is an abbreviation of Serving Gateway. The GGSN is a network gateway node responsible for the interworking between the GPRS core network and external packet switched networks, for example the Internet. The GGSN has Internet Protocol (IP) on both sides. Similarly, the PGW is a network gateway node responsible for the interworking between the Long Term Evolution (LTE) core network and external packet switched networks, for example the Internet.
The communications network comprises a mobility management node which may be a SGSN for 2G GSM and 3G UMTS access and MME for LTE access. The SGSN may further be classified to S4-SGSN (based on GTPv2) and Gn/Gp SGSN (based on GTPv1). The SGSN is a network node responsible for the delivery of data packets from and to the devices within its geographical service area. The SGSN provides control function and manages states, paging, authentication, mobility, roaming, and other bearer management functions. The SGSN is an access point for the device to the packet network. The SGSN understands radio access on one side and IP on the other side. The SGSN may be a S4-SGSN which is a SGSN which supports the S4 interface. The MME is a control node for the access network. The SGSN and the MME may be implemented in one physical node, and then it may be referred to as SGSN/MME. The SGSN and the MME may also be separate physical nodes. The term mobility management node is used in the following text in order to refer to the S4-SGSN, MME and the combined SGSN/MME.
As already indicated above, the PGW is a node which provides connectivity from the device to external packet data networks by being the point of exit and entry of traffic for the device. The SGW is a node which routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between Long Term Evolution (LTE) and other Third Generation Partnership Project (3GPP) technologies.
A Public Land Mobile Network (PLMN) is a network providing land mobile communications services to the public. The PLMN provides communication possibilities for devices. Each operator providing mobile services may have its own PLMN. Access to PLMN services is achieved by means of an air interface involving communications between devices. The PLMN is connected to the Public Switched Telephone Network (PSTN) in order to route calls. According to the 3GPP, a PLMN area is the geographical area in which a PLMN provides communication services to devices. In general the PLMN is limited by the borders of a country. Depending on national regulations there may be more than one PLMN per country.
The device may be located in and served by one PLMN and changes to another PLMN, i.e. it changes Serving Network (SN), for example when the device moves from one country to another country. PLMN change is one of SGW-CDR and PGW-CDR closure triggers and serving network, i.e. Serving Node PLMN Identifier, which indicates the serving node PLMN, Mobile Country Code (MCC) and Mobile Network Code (MNC), used during this record is an essential field in SGW-CDR and PGW-CDR. CDR, short for Charging Data Record, is a formatted collection of information about a chargeable event for use in billing and accounting. Examples of such chargeable event are time of call setup, duration of the call, amount of data transferred, etc. Both the MCC and the MNC are parts of the International Mobile Subscriber Identity (IMSI). CDRs may be classified with two parameters: 1) The node at which they are generated: GGSN, SGSN, PGW, SGW, etc. and 2) The type of service or activity they are charging: Multimedia Broadcast Multicast Services (MBMS), Mobility, Location request etc.
A serving network may be defined as a network that the device has registered with. The serving network may be identified with a serving network ID. The serving network may also be referred to as the serving PLMN. A device may register with more than one network at a time. A device may change from being served by a source serving network to being served by a target serving network, and consequently being registered with the same mobility management node or changing from being registered with a source mobility management node to a target mobility management node. In the following, the terms source is associated with a previous location of the device and the term target is associated with a current or future location of the device. The term old may be used instead of source and the term new may be used instead of target.
PLMN information is also important for Policy and Charging Control (PCC). To keep the SGW and PGW updated with the latest information about the serving network without side-effect, e.g., too much signaling, duplicated reporting caused, it is critical for a mobility management node to report information about the serving network precisely and smartly.
Two kinds of interfaces need to be updated to form a comprehensive solution for reporting information about the serving network.
Serving Network Change Reporting without Change of Mobility Management Node (Non-Mobility):
In the 3GPP specification, a delayed reporting mechanism is adopted for a device in idle mode whose procedure for intra-mobility management node serving network change does not inherently comprise sending, from the serving mobility management node, a Modify Bearer Request (MBR) message to the SGW and with the assumption that a service request procedure, where one modify bearer request message for each Packet Data Network (PDN) is mandatory, will be initiated when the device enters connected mode. Thus, a modify bearer request during a service request will anyway carry a serving network Information Element (IE) to the PGW via the SGW. The serving network IE is the identification of the serving network. This delayed reporting mechanism tends to avoid extra signaling to gateways. However, the service request procedure may not always happen when the device goes from idle to connected mode for some scenarios. The service request mentioned above is a procedure used by the device or the network to which there is uplink or downlink data to send, in order to establish radio access bearer.
In this non-mobility procedure, the mobility management node is a S4-SGSN or a combined SGSN/MME.
Intra-mobility management node serving network change, as mentioned above, refers to the case when the device changes serving network while still being connected to the same mobility management node, i.e. without changing mobility management node. This may also be referred to as a non-mobility procedure, since there is no change of mobility management node.
However, the service request procedure will not always happen when the device changes from idle mode to connected mode for some embodiments.
The 3GPP has agreed that the mobility management node shall include the serving network IE in the modify bearer request transmitted to the SGW only when the serving network has changed.
Meanwhile, the 3GPP SA2 has agreed that the serving PLMN change reporting may be delayed when the device is in ECM_IDLE state, i.e. in case the serving PLMN changes during intra-Tracking Area Update (TAU) with no user plane setup, the MME may report the changed serving PLMN to the SGW in the next Service Request procedure. ECM is short for Evolved packet system (EPS) Connection Management and ECM_IDLE is a state describing signaling connectivity between the device and the Evolved Packet Core (EPC). The device is in ECM_IDLE state when there is no Non Access Stratum (NAS) signaling connection between the device and the network. The device in ECM_IDLE state performs cell selection or reselection and PLMN selection.
In case of a tracking area update without the change of mobility management node, a change of serving network, Time Zone (TZ) or User CSG Information (UCI) is signaled in the next service request. This delayed reporting for an idle device applicable for a S4-SGSN, which is a SGSN supporting the S4 interface. The device initiated service request when Idle-mode Signaling Reduction (ISR) is not active, but the serving network has changed during previous mobility procedures, i.e. intra-mobility management node tracking area update/Routing Area Update (RAU) and the change has not been reported to the PGW yet.
CSG is short for Closed Subscriber Group. According to the 3GPP a closed subscriber group identifies subscribers of an operator who are permitted to access one or more cells of the PLMN but which have restricted access. The CSG may be identified with a unique identifier called CSG Identity (CSG ID), which is used by the device to facilitate access for authorized members of the CSG. The CSG ID is comprised in UCI. The UCI further comprises access mode and CSG membership indication. A CSG subscriber server may stores CSG subscription data for roaming devices.
The reporting principle in the 3GPP is clear that though the reporting of the serving network is mandatory, the potential signaling flooding towards the SGW and/or the PGW should be avoided, and it is not necessary to report the serving network change immediately when the device is in idle mode. However, with the existing approach for reporting the change of the serving network for idle devices, the SGW and/or the PGW will fail to get the latest information about the serving network in the following four scenarios:
(1) In Wideband Code Division Multiple Access (WCDMA), after the device performs intra-routing area update with serving network changes and returns to idle: In the subsequent service request, the S4-SGSN may selectively setup the Radio Access Bearer (RAB) for those bearer contexts having payload pending to save radio resource. Therefore, the serving network change is only reported to those PDN connections for which the S4-SGSN has setup a radio access bearer.
(2) In WCDMA, after the device performs intra-routing area update with the serving network changes and returns to idle: The PGW initiates a bearer create or bearer update or bearer delete operation, and the S4-SGSN may not setup user plane for other bearers. Thus, there will be no modify bearer request message within the procedure. After the Bearer create/update/delete, the SGW/PGW is not informed about the latest serving network.
(3) In WCDMA, when a direct tunnel is not used: There will be no modify bearer request in the service request procedure. Thus, the subsequent service request may not be relied on to report the serving network change.
(4) In Global System for Mobile Communications (GSM): There is no Service Request procedure, i.e. there is no additional modify bearer request message to be sent to the SGW when the device turns from idle to ready state according to the existing specification.
The direct tunnel mentioned above, is a feature that allows the mobility management node to establish a direct user plane tunnel between the radio access network, e.g. a Radio Network Controller (RNC) and the SGW.
Serving Network Change Reporting with Change of Mobility Management Node (Mobility):
3GPP states that, the serving network IE should be comprised in the forward relocation request message with the purpose of providing necessary information to the target mobility management node to judge when there is a change of serving network.
In case of inter-mobility management node idle mobility, e.g. tracking area update/routing area update, the target mobility management node may compare the PLMN in a Globally Unique Temporary ID (GUTI)/old Routing Area Identification (RAI) with the PLMN in the current Tracking Area Identity (TAI)/RAI. The TAI is the identity of the tracking area and the RAI is the identity of the routing area.
In the mobility procedure, the mobility management node is a S4-SGSN, a standalone MME or a combined SGSN/MME.
As mentioned above, inter-mobility management node serving network change refers to the case when the device changes serving network and also changes from being connected to a source mobility management node to a target mobility management node. This may also be referred to as a mobility procedure, since there is a change of mobility management node.
This information is not sufficient in order for the target mobility management node to know whether the latest information about the serving network has been reported to the gateway, i.e. SGW and PGW, or not.
During inter-mobility management node idle mobility, e.g. tracking area update/routing area update, the target mobility management node knows the PLMN used in source MME via GUTI, in the source mobility management node via/old RAI with the PLMN in the current TAI/RAI. During inter-mobility management node handover, the source mobility management node includes the serving network IE in a forward relocation request message to assist the target mobility management node to check when there is a serving network change which is the precondition of serving network reporting.
The target mobility management node compares the source serving network and target/current serving network, and takes futher action accordingly: When the serving network has changed, or when the mobility management node has not received any source serving network information from the source mobility management node, the mobility management node includes the new serving network IE in this message, i.e. the modify bearer request.
However, the target mobility management node does not have the knowledge whether the latest serving network information has been reported to the SGW or not, e.g. when the serving network of the device does not change, there is still possibility that the source mobility management node (e.g. SGSN/MME) has not reported information about the serving network to the SGW due to the “delayed reporting mechanism”.
Admittedly, as the existing 3GPP described, the target mobility management node will surely report the new serving network when it detects the serving network changes during the inter-mobility management node mobility without a SGW relocated procedure. But the target mobility management node will not report the current serving network when the serving network has not changed according to the condition specified in the current 3GPP specification. Based only on the the received serving network IE the target mobility management node will not be able to decide whether to report the information about the serving network or not in the case of the serving nework is not changed due to lack of the report status information which indicates when the source mobility management node has already reported the serving network or not to the SGW, as it is possible that the source mobility management node may have reported or have not reported it yet due to “Delay Reporting” mechanism for an idle device.
With this fact of lacking status report information, the target mobility management node will be in a dilemma of reporting or not for this unchanged serving network for those moving in devices. When the serving network is reported anyway, it may cause duplicated reporting thus unnecessary signalling load will ensue due to the speculation that the serving network unchanged mobility might be the most likely cases among all inter-mobility management node mobility cases. When the serving network has not been reported, then the serving network in the SGW/PGW may not be updated, consequently some problems will be caused, e.g., wrong information in the SGW-CDR and PGW-CDR.
Report of Time Zone and UCI
The aforementioned problem for reporting the serving network exists also for the report of Time Zone (TZ) and UCI. The time zone and the UCI are related to the device, i.e. the time zone in which the device is located and the UCI is related to the closed subscriber group to which the device belongs.